Variable transformer



May 20, 1958 R. VRADENBURGH ET AL 2,335,866

VARIABLE TRANSFORMER Filed June 10, 1954 2 Sheets-Sheet 1 INVENTO R5 7%! ATTORNEY y 20, 1958 R. VRADENBURGH EI'AL 2,835,866

VARIABLE TRANSFORMER 2 Sheets-Sheet 2 Filed June 10, 1954 INVENTORS 75 JusZznI/Ydmklti F0190? Wade/ h5g4 BY WA NEY m V. a I

United States Patent'O VARIABLE TRANSFORMER Robert Vradenburgh, Yonkers, and Justin J. Naviski,.

White Plains, N. Y.,-.assignors-.to Ward Leonard Electric Company, a corporation: of New York Application June 10, 1954, Serial No. 435,818

Claims. cram-47 This invention relates to autotransformers and is directed particularly to variable autotransformers wherein the voltage is variable in small steps from a maximum voltage to a minimum or zero voltage.

An object of this invention is to providea variable autotransformer that has'a high wattagerati'ng.

Another object ofthe invention is'to provide a variable autotransformer that is simple in construction.

Another object of theinvention is to provide a variable autotransformer that is inexpensive to manufacture and has a high wattage rating.

Another object of the invention is to provide a variable autotransformer that is dependable in operation'and durably resistant to shock.

A still further object of the invention is to provide a variable autotransforrner that dissipates heat and distributes localized heating to minimize. thetemperature use;

Other further objects and advantages will be apparent from the'following specification taken in connection with drawings, in which:

Fig. 1 is an end view of a variable autotransformer;

Fig. 2 is a sectional view of the variable autotransformer taken along lines 2-2 of Fig. 1;

Fig; 3 is an exploded view of the contact assembly and contact assembly head; and

Fig. 4-is a sectional view of the contact assembly and contact assembly head along lines 4-4 of" Fig. 2.

Referring toFig; 1", an autotransformer 10-is' shown having a toroidal'winding 11 connectedat the respective ends to line terminals 12', 13 bymeans of leads 14', 15. respectively. The windihg is intermediatel'y' connected from alternate windings to the cireumf'erentially arranged contacts 17 by'rneans' of the radially extending conducting resistance wires 19. The voltages are tapped" from the contacts 17 by the movable contact assembly 18 which successively connects-the contacts 17 to' the common collector means 20 which is in turn connected to the middle terminal 21 bythe metallic strap 22.

The autotransformer is" preferably circular" in shape and has a circular laminated core 24 having a' rectangular cross-section. The laminations preferably extend inan axial direction and are formed by circularly wrapping a thin ribbon of steel around itself from the innerdiameter of the core to the outer diameter or maybe round stocked steel laminae. The core is preferably insulated on all sides; An' insulating tape may be wrapped in overlapping turns around the core" to insulatethe winding 11 from the steel core 24 or other suitable insulating means may be used. The toroidal winding 11 is preferably made of double glass covered silcone copper wire of square cross-section and covers the core except for a portion adjacent the terminals 21, 12 and 13; The wire is toroidal wound around the core with alternate turns having a raised portion 27" projecting from the outer surface of the core. The inner portions of the turns are hank wound. The raised portion 27 'of the alternate turn is preferably generally triangular the autotransformer.

'ice

in shape with segment 27a at an acute angle to the outer surface of the insulated core with the apex of the angle adjacent the resistance wire end. The portions of the alternate winding turns that are along the side of the core' adjacent the apex of the angle preferably lie fiat against the insulation so that the support provided by the alternate winding turns will be applied in an even manner on the insulation.

The base plate 28 has a flat circular disc portion 2? and a lateral rim 30 around the outer edge of the disc portion 29 supporting the autotransformer It), the contacts 17', 17a, 17b and the terminal block 31 with terminals 21, 12, 13. The terminal block 31 is made of molded insulating material and is fastened on the outer rim by means of the central terminal 21, the nuts 34a and 34b threaded thereon and the washer 32. The terminals 12 and 13 areeach similar in construction and similarly molded in the block 31. The terminal 12 is a knurled screw machine part securely molded in the block 31. The lead 14 is fastened at one end to the terminal 12 by a lock'washer and nut and at the other end to the contact 17a. The lead 14 extends through the passage 37 molded in the insulator block 31 and is brazed or soldered to the contact 17a. The lead 15 is similarly connected to the terminal 13 and the contact 1712. The contacts 17a, 1722 are in turn connected to respective ends of the winding. 1-1 by resistance wires 19a; 19b.

A hearing hub 38 made of cold drawn seamless tubing is mounted through an opening in the center of thedisc portion 29- and fastened to the plate. 28' by the head 53 hearing against the inner surface of the disc portion 29 and. by the outer turned edge 36 which also clamps the stop 39-against the disc portion 29.-

An inset panel 41 is formed in the disc portion 29 'and' a tough, hard ground coat 42 with good surface adherihg properties such as a high grog content vitreous enamel is formed between the panel 41- and the rim- 30. Anembedding or covering layer 46 having high adhesive high heat conducting properties and of an inorganic material such as vitreous enamel is formed preferably extending from the rim 30 to the transformer and embeddingv the resistance wires 19, 19a,19b and the ends of contacts 17 to firmly bond them to the disc'portion 29 of the base plate 28 through the ground coat 42. The ground coat 42 and the'einbedding or covering layer 46 may hednade in accordance with the Patent No. 2,477,121 issued" to Charles J. Ganci on July 26; 1949;

The-fixed contacts 17 are in the form of a long rectangular block with flat wide contact surfaces '43; The contact surfaces 43 are parallel to the axis of the hub and circumferentially arranged in a diameter greater than the collector ring and spaced from the ring to form a channel between the ring and the contacts. The L-shaped resistance wires 19', 19a, 19b have the legs 44 extending radially with the outer ends brazed or silver soldered in notches in the ends of the contacts. The legs 44 and 45 are at an acute angle which is preferably in the order of eighty degrees. The legs 44 are generally parallel to the base plate 28 and the legs 45 are positioned to form a circular row of upstanding posts for supporting The contacts 17 are preferably radially aligned with the alternate raised windings of the autotransformer. The wires 19' are conductive members for passing high currents between the Winding and the contacts. The resistance of the wire limits the current between the short circuited contacts 17.

The ground coat is preferably formed in a thin layer on the base plate 28 and provides a surface with good adhering properties for bonding the embedding layer -46 thereto. The resistance wires 19 are held upright and the layer 46- in an amorphous form is spread covering the ends of the contacts 17 and embedding the legs 44 and the ends of the legs 45 of the resistance wire. The layer is fired forming a tough hard refractory layer that securely holds the wires 19 in place and strongly adheres to the ends of the circumferentially arranged contacts 17 and the radially arranged legs 44 of the resistance wires 19 to firmly secure the contacts 17 and the resistance wires to the base plate 28 and to transmit the weight of the autotransformer from the wires 19 to the base plate 28. The layers 42 and 46 have high heat conducting properties to remove the heat from the conducting resistance wires and the autotransformer 10.

The alternate windings of the autotransformer 10 have segments 27 raised from the core 24 to engage the end portion of the upstanding legs 45. The insulation on each outer surface of the raised segment is removed and the segments 27a are brazed or silver soldered to .the electrically contacting end portions of the legs 45.

The wires 19 are stiff and with the leg 44 embedded in the vitreous enamel layer 46 ample support for the autotransformer is provided spacing it from the ground coat 42. The resistance wires 19 may be made of a chromium nickel alloy and provide a resistance between the windings and the contacts to limit the short circuited loop current through the short circuited contacts and the short circuited windings of the autotransformer 10. The weight of the laminated iron core is distributed through the alternate windings of the transformer to the embedded supporting resistance wires and is transmitted to the base plate through the vitreous enameled insulating layers. It is preferable that the resistance wires are circumferentially distributed to provide a uniform support around the periphery of the autotransformer.

Instead of the supporting wires providing the resistance between the shorted turns carbon brushes may be used to limit the current and the wires 19 may be of a good conductive metal having the rigidity and strength to support the autotransformer.

The collector ring base plate 20 stamped from brass sheet comprises a disc portion 48 with a center opening and annular rim 49 turned from outer edge of the disc portion. The collector ring plate is conventionally positioned within the contacts 17 and forms an enclosing cover for the autotransformer and the projecting legs 45 of the resistor wires. The exterior surface of the rim 49 forms a common collector ring and is radially spaced from the contacts 17 to form a circular groove or channel 26. The space within the plate 20 is filled with refractory or other inorganic cement 51 completely embedding the autotransformer 10 and the projecting legs 45 to insulate the autotransformer and legs from the plate 20 and adhere the collector ring plate 20 and the autotransformer 10 together and through the vitreous enamel cover coat 46 to the ground coat 42 and the inset panel 41. The embedding layer is preferably a titanium zircon cement or other inorganic cement with good heat conducting properties and in conjunction with the ring plate 20 permits a high overall and hot spot temperature rise. The collector ring plate 20 is substantially coextensive in area to the side and outer peripheral surface of the autotransformer and in cooperation with the base plate 28 distributes the heat created by a localized temperature rise, thus forming a potted coil enclosure.

The annular metallic surface 49 is concentric to the bearing hub forming a continuous contacting surface for the contact assembly rotating about the axis of the surface 49 and is polished so that the contact assembly makes good conductive contact with the collector ring. The U-shaped copper strap 22 along leg 52 is brazed or silver soldered to the surface 49 and the leg 53 fastened to the terminal 21.

The contacts 17 are concentrically arranged around the axis of the bearing hub 38 with the contact surfaces 43 formed in an annular ring parallel to the axis of rotation of the contact assembly 18. As previously deassume scribed the ends of the contacts 17 are brazed or soldered to the resistance wires 19 and embedded in the covering layer 46 to secure the contacts to the disc portion 29. The covering layer or resistor cover coat is a vitreous enamel or other high adhesive, high heat conductive inorganic material. The contacts 17 are further secured to the base plate 28 by the circular layer 55 of refractory cement. The cement is filled in between the rim 30 and the contacts 17 embedding the outer peripheral surfaces and the sides of the contact to further adhere the contacts to the rim 30 and the covering layer 46, thus retaining the contacts in place. The cement is preferably titanium zircon or other inorganic type. The contact surfaces 43 projecting beyond the surface of the cement are engaged by the contact assembly 18. In assembling, the contacts 17 are held in position by a common circular member (not shown) and the resistance wires 19 to which they are brazed or otherwise bonded. The common member is cut off after the cement layer 55 is set. The tops of the contacts are then cut down on a level with the layer 55. At the terminal block 31 the cement layer circumferentially ends at the washer 32. The inserts 56 and 57 extend through the rim 30 into the ends of the layer 55. The leads 14, are embedded in the layer 55 and connected in the vitreous enamel to the resistance wires 19a, 19b through segments 17a and 17b. Bolts 58 and 59 are mounted in the. plate 28 and extend into the ground coat and the vitreous enamel layer in the space between the ends of the row of resistors.

The base plate is a stamped sheet of steel and has a disc portion 29 and a rim portion 30. The collector ring is concentrically mounted within the rim and spaced therefrom by the channel 26, contacts 17 and the insulating layer 55. The bearing hub 38 is axially mounted through the titanium zircon cement encasing the autotransformer 10. The hub is fastened to the plate 29 by the bead 53 bearing against the inner surface of the plate 29 and the turned edge 36 which also clamps the stop 39 against the disc portion 29. The stop 39 is indexed by the projection fitting into an opening in the disc 29. A hearing sleeve 47 fits inside the hub 38 to provide a smooth bearing surface for the shaft 60 journaled in the sleeve. The arm 61 is mounted on the shaft 60 by means of the coupling member 63, bolts 64 and name plate 65. The arm 61 is preferably made from cast aluminum and has a disc shaped hub portion 66 at one end of the arm. The hub portion 66 has studs 66a, 66b snugly fitting into openings in the coupling member with the bolts 64 threaded in the coupling member through the studs and bear against the name plate to hold the hub on the coupling member.

The contact assembly 18 comprises a U-shaped brush holder 71 made of sheet steel and having flanges 72 and 73 for fastening the member 71 to the insulator by means of bolts extending through the openings 74. The side 76 has slots 78 through which the stranded copper wire 80 connecting the brushes 81 and 82 extends. The brushes are stacked back to back and each pair is spring loaded by a spring 83. The insulator block 70 is made of glass bonded mica and has beads 74 on the upper surface fitting around the head 67 of the arm 61, and beads 56 between which the flanges 72, 73 of the brush holder are recessed. The contact assembly 18 is thereby firmly held by the arm 61. The shaft 60 rotating the arm 61 and the brush assembly 18 is turned by the hub 87 keyed to the shaft 60. The shaft '60 is held firmly against axial movement by the pin 88 extending through shaft 60 on the disc portion 28 side and by the coupling member 63. An arm 89 is mounted on the shaft 60 between the pin 88 and the hub 87 and extends radially therefrom to engage projection 90 on the stop 39. The stop 39 and arm 89 limit the rotation of the contact assembly 1.8 so that it does not override.

It is thus seen that the resistance wires 19 are utilized to support the autotransformer 10 without the refractory "gens-see cement and also to connect the alternate turns of the autotransformer to the contacts 17. The wire 19 also introduces resistance between shorted contacts 17 and the closed transformer Winding so that the circulating current through the loop is limited to a harmless value.

In the preferred embodiment the contacts 17 are annularly positioned with the contact surfaces facing the Winding. In other embodiments the resistance wires support the winding in a comparable manner by having a portion of each wire embedded in an inorganic high adhesive, high heat resistant cement layer and the other portions formed to provide a multiplicity of supports attached to the winding at spaced points.

The variable autotransformer is normally positioned vertically and supported by means of the mounting brackets 91 fastened to the rim 30. The hub portion of the arm 61 balances the head 67 and the contact assembly 18 at the other end of the arm 61. The contact assembly 18 is held at the desired position by clamping shaft 60 through the actuating means that adjust the contact assembly 18 to the desired position. The Weight of the transformers is primarily transferred to the mounting plate 28 by the wires 19 and refractory layers 42, 46. The transformer may also be secured to the disc portion 29 by the embedding cement layer 51 adhering to the layer 42 and thus to the disc portion 29. Thus the weight is transmitted through the vitreous enamel layer to the base plate and thereby to the mounting brackets 91'. The resistance wires 19 support the autotransformer without the cement layer 51.

The collector ring plate shields the cement layer against abuse and distributes the heat generated in the autotransformer. The winding 11 is separated from the collector plate Zil by the thin layer of cement 93 on one side and from the base plate 28 by layers of cement 42 and 94 on the other side. Thus on both sides of the autotransformer there are large heat conducting areas to distribute any localized heating and increase the capacity of the transformer. Heat is also distributed by the collector surface which is spaced from the windings of the autotransformer by the cement layer 95. The resistance wires 19 also provide a heat path to the contacts 17. The resistance wires 19 provide access to the autotransformer transferring heat to the outer radial surface of the plate 29. The legs .4 fan out from the autotransformer providing this additional heat transfer. The embedding of the supporting resistors and the autotran'sform'er in the vitrous enamel layer and the titanium zircon cement layer permits an overall higher temperature rise of the unit. Thus on three sides, the autotransformer has metallic conducting surfaces adjacent therefrom to increase the capacity of the variable autotransformer. The laminations of the core 24 also provide a heat path for the distribution of any localized heating. The contact surfaces 43 also distribute heat created at the brush contacting surfaces. The brush contactors 82 can transmit the heat through the brush holder 71 or through the contacts 17 to rim 30.

One of the advantages of the aforementioned described structure is that the autotransformer may be operated at a high wattage. This advantage accrues from the enclosure of the autotransformer in a refractory cement and providing a metallic shield around the embedding cement. Such a construction reduces the temperature rise of hot spots occurring on the transformer windings. The resistor wires connecting the autotransformer to contacts 11 are embedded in the vitreous enamel layer which increases the wattage rating at which these connecting wires may be operated. The entire load current passes through one or two of the resistance wires at one time. Therefore, these resistance wires dissipate a great deal of power. The embedding of the resistance wires in an insulation having good heat conducting properties such as vitreous enamel permits a high temperature rise and therefore a corresponding high wattage rating.

Various modifications may be made in the preferred embodiment describedin the above specification without departing from the scope of the invention.

We claim:

1. An electrical control apparatus comprising mounting means having a metallic heat conductive plate with a lateral rim, a core, a winding on said core, contact surfaces separate from said winding and arranged adjacent to said rim and in a row facing said winding, said contact surfaces spaced therefrom to form a channel for a contact assembly, and conductive members extending in a plane generally parallel to' the conductive plate from said stationary contact surfaces to turns of said winding to interconnect said winding and said contact surfaces for successively tapping incrementally different voltages from said contact surfaces.

2. A variable transformer comprising mounting means, a circular core, a winding thereon with alternate windings having an outwardly radially projecting segment, an inorganic, high heat resistant, high adhesive cement formed ina layer on said mounting means, a plurality of circumferentially arranged resistance wires each having a portion embedded in said layer of cement and a second portion projecting out of said layer at an angle extending from said mounting means and. attached to said segment for supporting the winding.

3; A variable transformer comprising mounting means having a metallic heat conductive plate with a lateral rim, a core, a winding on said core and having segments of turns formed in a row, stationary contact surfaces arranged adjacent to said rim and in a row facing said row of segments and spaced therefrom to form a channel for a contact assembly, conductive members extending in a plane generally parallel to the conductive plate and from said. contact surfaces to said segment to interconnect said winding and said contact surfaces for successively tapping incrementally different voltages from said contact surfaces and a second conductive member in said channel between said segments and said contact surfaces to remove said voltages.

4. A variable transformer comprising mounting means having a metallic heat conductive plate with a lateral rim, a core, a winding, contact surfaces arranged adjacent to saidv rim and in a row facing said winding and spaced therefrom to form a channel for a contact assembiy, conductive members extending and in a plane generally parallel to the conductive plate from said stationary contact surfaces to said winding successively to tap incrementally different voltages from said contact surfaces and connected to said winding at spaced points to distributively support the autotransformer' winding.

5. A variable transformer comprising a core, a winding on said. core having segments formed in a row, contact surfaces arranged in a row facing said row of segments and spaced therefrom to form a channel for a contact assembly, supporting conductive members extending from said stationary contact surfaces to said segments to interconnect said winding and said contact surfaces for successively tapping incrementally different voltages from said contact surfaces, a layer of vitreous enamel, said conductive members having a portion embedded in said layer of vitreous enamel in contact with said contact surfaces and a second portion at an angle to said first portion and connected to respective segments to support said autotransformer. V

6. A variable transformer comprising mounting means, a core, a winding on said core with segments of turns formed in a row, contact surfaces spaced therefrom and facing said winding, conductive members formed in a row with each conductive member having a first portion and a second portion at an angle to said first portion extending away from said mounting means, a cement layer, each of said first portions securely and electrically fastened to a respective segment, each of said second portions electrically connected to a respective contact surface and embedded in said refractory cement layer to firmly secure said conductive members together and to said layer to provide a unitary support for said core and winding electrically interconnecting each segment to a respective contact surface.

7. A variable transformer comprising mounting means, a circular metallic ring shaped core having a toroidal winding with segments of turns circumferentially arranged around the outside of the core, contacts arranged parallel to the axis of the core and radially spaced from the segments to form a channel in which a contact assembly travels, metallic members interconnecting said winding and said contacts for successively tapping incrementally different voltages from said winding, each of said members having a radially extending portion connected to said contact and a second portion at an angle to said first portion and joined to alternate segments, a vitreous enamel layer embedding said first portion to bond said members to said mounting means so that said conductive means through said second portion supports said winding and core.

8. A variable transformer comprising a circular ring shaped metallic core rectangular in section, a wire toroidally wound on said core with outer circumferentially arranged and uniformly spaced segments generally paral lel to the axis of the core, contacts circumferentially arranged around said winding parallel to the axis of said core, said contacts radially spaced from said segments to form a groove for accommodating a contact assembly between said contacts and segments, a collector ring between said contact and said segments and having an annular surface facing said contacts forming a groove for accommodating a contact assembly continuously engaging said contact to successively engage said contact and successively tap incremental voltages.

9. A variable transformer as claimed in claim 7 in which a contact assembly is provided in said groove and having a pair of electrically interconnected brushes in resilient back to back relation, one brush engaging a contact and the other brush to transmit the contact voltages to said collector ring plate.

10. A variable transformer as claimed in claim 7 wherein metallic resistance members extend radially and substantially have a portion connected to said contact at one end and a second portion at an angle to said first portion and firmly connected to alternate segments of the winding, vitreous enamel layer embedding said first portion to securely holdsaid resistance members and support said winding.

11. A variable transformer comprising a circular steel base plate having a lateral annular rim around the outer edge and a ground coating of insulating material, an autotransformer having a ring shaped steel core with a toroidal winding positioned concentrically within said base plate, contacts circumferentially arranged around said winding and radially spaced to form a channel, L- shaped conductive resistance wires circumferentially distributed around said winding with a first portion connected to alternate turns and a second portion at right angles thereto projecting radially outwardly to engage said contacts, a circular collector ring plate with a lateral annular outer rim concentrically positioned over the winding with the rim outwardly spaced between said winding and said contacts metallically enclosing said winding, said rim forming a groove with said contacts, a refractory cement filling the space between the collector ring plate and the ground coat to embed the autotransformer, a contact assembly having conductive means successively interconnect ing said contacts and the rim of the collector ring plate 8 t rotatable about the axis of the core and successively tapping incremental voltages from contact, said collector ring plate forming a heat conducting means to distribute temperature rise in said winding.

12. A contact assembly for simultaneously engaging a continuous annular collector ring surface and contacts spaced therefrom to form a channel therebetween comprising an insulating member mountable on one side to an arm, a U-shaped brush holding member having parallel walls, brushes slidably positioned between said walls in back to back relation with contact surfaces facing in opposite directions to engage said collector ring surface and said contacts respectively, resilient means between said walls and pressing the back to back brushes radially against the respective collector ring surface and contact surfaces, slots in one of said walls adjacent a respective brush, and a flexible stranded wire extending through the slots and outside of said wall to interconnect back-to-back brushes for carrying the current passing between the brushes.

13. Electric controlling apparatus comprising a core, a winding thereon, a series of fixed contacts having contact surfaces facing said Winding, a series of resistors electrically connected between said contacts and turns of said winding, a metallic casing enclosing said Winding and including a metallic collector wall between said winding and said contact surfaces, insulating material embedding said winding and resistors, and movable contact means for successively engaging said contact surfaces and engaging said collector wall between said contact surfaces and said winding.

14, Electric controlling apparatus comprising a core, a winding thereon, a series of fixed contacts spaced from and facing said winding, a series of resistors electrically connected between said contacts and turns of said winding, a metallic member between said winding and contacts to form a common collector ring, a second metallic member adjacent said winding enclosing said winding in cooperation with said first metallic member, insulating material filling the enclosed space and completely embedding said winding and resistors, and movable contact means simultaneously engaging said first metallic member and said contacts,

15. A variable transformer comprising a circular steel base plate, a ground coating of insulating material, an autotransformer having a ring-shaped steel core with a toroidal winding, contacts arranged around said winding and radially spaced to form a channel, L-shaped conductive resistance wires distributed around said winding with a first portion connected to alternate turns and a second portion at right angles thereto projecting radially outwardly to engage said contacts, a collector ring plate with a lateral annular outer rim concentrically positioned over the winding with the rim outwardly spaced between said winding and said contacts metallically enclosing said winding, a refractory cement filling the space between the collector ring plate and the ground coat to embed the autotransformer, a contact assembly having conductive means successively interconnecting said contacts and the rim of the collector ring plate rotatable about the axis of the core and successively tapping incremental voltages from contact, said collector ring plate forming a heat conducting means to distribute temperature rise in said windmg.

References Cited in the file of this patent UNITED STATES PATENTS 2,201,881 Bryant et al May 21, 1940 2,265,667 Mekelburg ct al. Dec. 9, 1941 2,555,103 Andrews May 29, 1951 

